Observation of a ppb mass threshoud enhancement in \psi^\prime\to\pi^+\pi^-J/\psi(J/\psi\to\gamma p\bar{p}) decay

TL;DR

This paper reports the observation of a threshold enhancement in the proton-antiproton invariant mass spectrum from $oldsymbol{\psi^\prime ooldsymbol{\pi^+\pi^-J/oldsymbol{\psi}} ext{ with }J/oldsymbol{\psi} ooldsymbol{\gamma par{p}}$ decays, indicating a possible new resonance.

Contribution

First observation of a ppb mass threshold enhancement in $oldsymbol{\psi^\prime}$ decays with detailed mass and width measurements.

Findings

Enhancement observed at 1861 MeV/c^2

Resonance width is less than 38 MeV/c^2

Results are consistent with previous BESII findings

Abstract

The decay channel $\psi^\prime\to\pi^+\pi^-J/\psi(J/\psi\to\gamma p\bar{p})$ is studied using a sample of $1.06\times 10^8$ $\psi^\prime$ events collected by the BESIII experiment at BEPCII. A strong enhancement at threshold is observed in the $p\bar{p}$ invariant mass spectrum. The enhancement can be fit with an $S$-wave Breit-Wigner resonance function with a resulting peak mass of $M=1861^{+6}_{-13} {\rm (stat)}^{+7}_{-26} {\rm (syst)} {\rm MeV/}c^2$ and a narrow width that is $\Gamma<38 {\rm MeV/}c^2$ at the 90% confidence level. These results are consistent with published BESII results. These mass and width values do not match with those of any known meson resonance.